CN110635696A

CN110635696A - Power supply switching circuit and switching method

Info

Publication number: CN110635696A
Application number: CN201810663433.3A
Authority: CN
Inventors: 粘家荣; 苏志凱
Original assignee: Delta Optoelectronics Inc
Current assignee: Delta Electronics Inc; Delta Optoelectronics Inc
Priority date: 2018-06-25
Filing date: 2018-06-25
Publication date: 2019-12-31
Also published as: EP3588763A1; US10862400B2; EP3588763B1; US20190393793A1

Abstract

The invention provides a power switching circuit and a switching method thereof. The transformer is used for outputting a first power signal and is provided with a middle tapping end. The rectifying unit is coupled to the transformer, receives the first power signal and outputs a second power signal. The first switching unit is coupled to the rectifying unit and the middle tap end of the transformer. The second switching unit is coupled to the rectifying unit and the first switching unit. The feedback unit receives the second power signal and is used for controlling the first switching unit and the second switching unit.

Description

Power supply switching circuit and switching method

Technical Field

The present disclosure relates to a power switching circuit and a switching method thereof, and more particularly, to a power switching circuit disposed in a power conversion device.

Background

With the development of power electronics, power conversion devices are widely used in many power conversion devices. With the trend of different requirements, the resonant power device needs wider output modulation to supply loads with different requirements.

In the conventional power converter, a control unit transmits a control signal to a primary side switch and outputs Pulse Width Modulation (PWM) to control the primary side switch to switch, thereby achieving the purpose of outputting voltage in a wide range.

Disclosure of Invention

The invention relates to a power supply switching circuit, which comprises a transformer, a rectifying unit, a first switching unit, a second switching unit and a feedback unit. The transformer is used for outputting a first power signal and is provided with a middle tapping end. The rectifying unit is coupled to the transformer, receives the first power signal and outputs a second power signal. The first switching unit is coupled to the rectifying unit and the middle tap end of the transformer. The second switching unit is coupled to the rectifying unit and the first switching unit. The feedback unit receives the second power signal and is used for controlling the first switching unit and the second switching unit.

An embodiment of the disclosure provides a switching method of a power switching circuit, the power switching circuit includes a transformer, a rectifying unit, a first switching unit and a second switching unit, the transformer includes a middle tap, the rectifying unit is coupled to the transformer, the rectifying unit is configured to provide a second power signal, the first switching unit is coupled between the middle tap and a load, and the second switching unit is coupled between the rectifying unit and the load.

In summary, the power switching circuit and the switching method thereof of the present invention can be disposed in different resonant converter architectures according to actual requirements, and the feedback unit receives the magnitude of the power signal output by the rectifying unit to control the on/off of the first switching unit and the second switching unit, so that the rectifying unit can operate in a full-bridge rectification type or a half-bridge rectification type according to different load requirements, and achieve the purpose of wide output voltage range, and the feedback unit only controls the on/off state of the switch, so that the power switching circuit has no switching loss during switching.

Drawings

Fig. 1 is a functional block diagram of a power converter according to an embodiment of the present disclosure.

FIG. 2 is a further circuit diagram of a power converter according to an embodiment of the present disclosure.

Fig. 3 is an enlarged schematic diagram of a transformer winding structure according to an embodiment of the disclosure.

FIG. 4 is a timing diagram of the power switching circuit according to an embodiment of the disclosure.

FIG. 5 is a timing diagram of the power switching circuit according to an embodiment of the disclosure.

FIG. 6 is a timing diagram of the power switching circuit according to an embodiment of the disclosure.

FIG. 7 is a timing diagram of the power switching circuit according to an embodiment of the disclosure.

FIG. 8 is a schematic diagram of another embodiment of a power switching circuit according to an embodiment of the present disclosure.

FIG. 9 is a circuit diagram of another embodiment of a power switching circuit according to the present invention.

FIG. 10 is a circuit diagram of another embodiment of a power converter according to the present disclosure.

Wherein, the reference numbers:

100 power converter

110 resonant circuit

200 power supply switching circuit

210 transformer

211 main winding

212 first secondary winding

213 second sub-winding

214 middle tap end

220 rectifying unit

230 feedback unit

240 first switching unit

250 second switching unit

D1, D2, D3 and D4 diodes

C1 capacitance

Cr resonant capacitor

Cr1 first resonant capacitor

Cr2 second resonant capacitor

Q1 first switch

Q2 second switch

Q3 third switch

Q4 fourth switch

V1 first Power Signal

V2 second Power Signal

CS1, CS2 induction current element

300 load

Detailed Description

The terms "comprising," having, "" including, "and the like, as used herein, are intended to be open-ended terms that mean" including, but not limited to. Further, as used herein, "and/or" includes any and all combinations of one or more of the associated listed items.

In this document, when an element is referred to as being "connected" or "coupled," it can be referred to as being "electrically connected" or "electrically coupled. The term "connect" or "couple" can also be used to indicate that two or more elements are in mutual engagement with each other for operation or interaction. Furthermore, although the terms first, second, …, etc. may be used herein to describe various elements, these elements and operations are used only to distinguish one element from another or from another element or operation described in the same technical field. Unless the context clearly dictates otherwise, the terms do not specifically refer or imply an order or sequence nor are they intended to limit the invention.

Referring to fig. 1, fig. 1 is a functional block diagram of a power converter 100 according to an embodiment of the present disclosure, wherein the power converter 100 is configured to supply power to a load 300. The power converter 100 includes a resonant circuit 110 and a power switching circuit 200. The power switching circuit 200 is coupled between the resonant circuit 110 and the load 300, and the power switching circuit 200 is used for converting the resonant power output by the resonant circuit 110 into an output voltage required by the load.

As shown in fig. 1, the power switching circuit 200 further includes a transformer 210, a rectifying unit 220, a feedback unit 230, a first switching unit 240, and a second switching unit 250. The transformer 210 converts the resonant power provided by the resonant circuit 110 and is used to output a first power signal V1. The rectifying unit 220 receives the first power signal V1 and generates a second power signal V2, the second power signal V2 is used for driving the load 300. The first switching unit 240 and the second switching unit 250 are coupled between the rectifying unit 220 and the load 300. In one embodiment, the feedback unit 230 is used to control the switching states of the first switching unit 240 and the second switching unit 250, so that the rectifying unit 220 operates in different working states. When the rectifying unit 220 is in different operating states, the second power signal V2 can have different voltage output ranges, so that the power switching circuit 200 can support a wider range of output voltages.

Referring to fig. 2, a further circuit diagram of the power converter 100 in fig. 1 according to an embodiment of the disclosure is shown, as shown in fig. 2, the power switching circuit 200 further includes a capacitor C1 and a sense current element CS 1. In the embodiment of fig. 2, the sense current element CS1 may include a resistor, and in the embodiment of fig. 2, the feedback unit 230 may measure the magnitude of the current passing through the sense current element CS1 and the magnitude of the voltage of the second power signal V2 to control the switching states of the first switching unit 240 and the second switching unit 250.

The capacitor C1 is coupled between the positive terminal and the negative terminal of the output side for stabilizing the output voltage of the power converter 100 to the load 300.

In which the resonant circuit 110 shown in fig. 2 is a half bridge LCC resonant circuit, resonant power can be output. The half-bridge LCC resonant circuit shown in fig. 2 is only used as an example, but not limiting the invention, the resonant circuit 110 can be a full-bridge LLC resonant circuit, a half-bridge LLC resonant circuit, a full-bridge LCC resonant circuit, a half-bridge LCC resonant circuit, a quasi-resonant circuit, etc., and the resonant circuit 110 can be configured differently according to actual requirements.

In some embodiments, the resonant circuit 110 as shown in FIG. 2 may include a resonant capacitor Cr. The resonant circuit 110 has a charging and discharging function by the resonant capacitor Cr, so that the resonant circuit generates resonant power and transmits the resonant power to the secondary side of the transformer 210 through the transformer 210.

When the transformer 210 receives the power output from the resonant circuit 110 and outputs the first power signal V1 to the rectifying unit 220, the rectifying unit 220 converts the first power signal V1 into the second power signal V2, and transmits the second power signal V2 to the load 300 for supplying the load 300 with the power required by normal operation. In addition, the feedback unit 230 can detect a voltage level (and/or a current level) of the second power signal V2, and the feedback unit 230 selectively turns on or off the first switching unit 240 and the second switching unit 250 according to the received second power signal V2.

In some embodiments, referring to fig. 3, an enlarged schematic view of the winding structure of the transformer 210 in fig. 2 according to an embodiment of the disclosure is shown. Referring to fig. 2 and fig. 3, the transformer 210 structurally includes a primary winding 211 on the primary side, a first secondary winding 212 on the secondary side, and a second secondary winding 213, wherein the primary winding 211 on the primary side is coupled to the resonant circuit 110, and the first secondary winding 212 on the secondary side and the second secondary winding 213 on the secondary side are coupled to the rectifying unit 220. The connection of the first secondary winding 212 and the second secondary winding 213 also forms an intermediate tap end 214. The transformer 210 is used for providing a first power signal V1 to the rectifying unit 220 according to the output power of the resonant circuit 110.

As shown in fig. 2, the rectifying unit 220 is composed of diodes D1, D2, D3 and D4, and an anode terminal of the diode D1 is coupled to a cathode terminal of the diode D2 and to an upper side (not a central tap end) of the first secondary winding 212 of the transformer 210. The cathode terminal of the diode D1 is electrically coupled to the cathode terminal of the diode D3. The anode terminal of the diode D2 is electrically coupled to the anode terminal of the diode D4, and the cathode terminal of the diode D4 is electrically coupled to the anode terminal of the diode D3 and to the lower side (the other non-central tap terminal) of the second secondary winding 213. The cathode terminal of the diode D1 and the cathode terminal of the diode D3 are electrically coupled to the first terminal of the capacitor C1 and the load 300.

In some embodiments, as shown in fig. 1 and fig. 2, the rectifying unit 220 in the power converter 100 may output the second power signal V2 to the load 300, and in general applications, the load 300 may have different characteristics or different operation modes, for example, the load 300 may be a low-power electrical appliance (e.g., a small-sized lamp, a mobile phone charger), or a large-power electrical appliance (e.g., a washing machine, a cold air), or even a larger-power device (e.g., a large-sized communication device, a cloud server), and generally different specifications of the power switching circuit need to be designed for loads 300 with different power consumptions. The power converter 100 generally has a certain output power range, and in order to achieve a larger support range, a complex circuit, a passive element with a larger operation range, or a power chip is usually required, which results in disadvantages such as increased production cost and larger power loss.

In some cases, the power consumed may vary significantly because the load 300 operates under different conditions, such as full speed operation, low speed operation, or standby mode of the manufacturing equipment, and different power requirements may be required for different machines. In the present disclosure, the power switching circuit 200 disposed in the power converter 100 can dynamically adjust the operation mode of the rectifying unit 220 to automatically switch between the full-bridge rectifying mode and the half-bridge rectifying mode, so that the same rectifying unit 220 can correspond to a wider range of output voltages. How to dynamically adjust the rectifying unit 220 is described in detail below.

In some embodiments, the feedback unit 230 has a function of receiving the second power signal V2 and analyzing the second power signal V2, and outputs different control signals according to the second power signal V2. The feedback unit 230 is coupled to the first switching unit 240 and the second switching unit 250, and the feedback unit 230 can enable the first switching unit 240 and the second switching unit 250 to be selectively turned on or off by the output control signal.

In some embodiments, the feedback unit 230 is configured to receive the second power signal V2 output by the rectifying unit 220, and compare the second power signal V2 with a preset voltage reference to output a control signal to selectively turn on or off the first switching unit 240 and the second switching unit 250. For example, the voltage reference is a reference voltage that is usually set for the internal circuit of the feedback unit 230, and the voltage reference may be set to different voltage values due to different actual requirements.

In the embodiment shown in fig. 2, the first switching unit 240 includes a first switch Q1, and the second switching unit 250 includes a second switch Q2. The first switch unit 240 and the second switch unit 250 of the present disclosure are not limited to the mosfet switches (the first switch Q1 and the second switch Q2) shown in fig. 2, and in other embodiments, the first switch unit 240 and the second switch unit 250 may also be bipolar transistor switches or other circuit elements capable of switching between on and off states.

For simplicity of description, in the following embodiments, the on or off states of the first switch Q1 and the second switch Q2 shown in fig. 2 are mainly adopted to illustrate the operation modes of the first switching unit 240 and the second switching unit 250, and it is within the technical scope of the present invention to replace the first switch Q1 and the second switch Q2 with other equivalent switching circuit elements.

As shown in the embodiment of fig. 2, a first terminal (e.g., the left terminal in fig. 2) of the first switch Q1 is coupled to the middle tap of the transformer 210, a control terminal of the first switch Q1 is coupled to the feedback unit 230, and a second terminal (e.g., the right terminal in fig. 2) of the first switch Q1 is coupled to the load 300. A first terminal (e.g., a left terminal in fig. 2) of the second switch Q2 is coupled to the anode terminal of the second diode D2 and the anode terminal of the fourth diode D4, a control terminal of the second switch Q2 is coupled to the feedback unit 230, and a second terminal (e.g., a right terminal in fig. 2) of the second switch Q2 is coupled to the load 300 and a second terminal of the first switch Q1.

The feedback unit 230 detects the second power signal V2 to be output to the load 300, and in practical applications, when the voltage required by the load 300 is large (for example, when the machine of the manufacturing equipment operates at full speed), the feedback unit 230 of the present disclosure turns on the second switch Q2 and turns off the first switch Q1. Referring to fig. 4 and 5, fig. 4 is a schematic diagram illustrating a current flow of the power switching circuit 200 shown in fig. 1 when the first switch Q1 is turned off and the second switch Q2 is turned on. Fig. 5 is a schematic diagram illustrating another current flow direction of the power switching circuit 200 in fig. 1 when the first switch Q1 is turned off and the second switch Q2 is turned on.

As shown in fig. 4, since the first switch Q1 is controlled by the feedback unit 230 to be turned off, and the second switch Q2 is controlled by the feedback unit 230 to be turned on, when the current path from the transformer 210 to the load 300 flows through the first secondary winding 212 from the second secondary winding 213, the current flows through the diode D1, the capacitor C1, the load 300, the inductive current element CS1, the second switch Q2, and the diode D4, and under such a current path, the rectifying unit 220 operates in a full-bridge rectification mode. In this case, the rectifying unit 220 rectifies the upper side of the first secondary winding 212 and the lower side of the second secondary winding 213, so the rectifying unit 220 can extract an output voltage difference of the complete secondary side of the transformer 210. The rectifying unit 220 outputs a second power signal V2 with a larger voltage, and the second power signal V2 is filtered by the capacitor C1 and then transmitted to the feedback unit 230, so that the second power signal V2 is sufficient to drive the load 300 with a larger power demand.

As shown in fig. 5, since the first switch Q1 is controlled by the feedback unit 230 to be turned off, and the second switch Q2 is controlled by the feedback unit 230 to be turned on, when the current path from the transformer 210 to the load 300 flows from the first secondary winding 212 through the second secondary winding 213, the current flows through the diode D2, the diode D3, the capacitor C1, the load 300, the inductive current element CS1, and the second switch Q2. Fig. 4 and 5 are schematic diagrams of the rectifying unit 220 under the full-bridge rectification mode, and the differences are only that the transformer current direction is opposite and the current flows through the diodes.

In other cases, when the load 300 requires a smaller voltage (e.g., the machine of the manufacturing facility is operating at a low speed or in a standby state, or the load 300 is a small electrical appliance or a small machine), the feedback unit 230 detects the second power signal V2 to be output to the load 300, and the feedback unit 230 may detect that the voltage of the second power signal V2 is smaller. The feedback unit 230 of the present invention turns off the second switch Q2 and simultaneously turns on the first switch Q1. Referring to fig. 6 and 7 together, fig. 6 is a schematic diagram illustrating one current flow of the power switching circuit 200 in fig. 1 when the first switch Q1 is turned on and the second switch Q2 is turned off. Fig. 7 is a schematic diagram illustrating another current flow direction of the power switching circuit 200 in fig. 1 when the first switch Q1 is turned on and the second switch Q2 is turned off.

As shown in fig. 6, since the first switch Q1 is controlled by the feedback unit 230 to be turned on and the second switch Q2 is controlled by the feedback unit 230 to be turned off, when the current path between the transformer 210 and the load 300 flows from the middle tap end 214 to the upper side of the first secondary winding 212, the current flows through the diode D1, the capacitor C1, the load 300, the inductive current element CS1 and the first switch Q1, and the rectifying unit 220 operates in a half-bridge rectification mode under such a current path. In this case, the rectifying unit 220 rectifies the upper side and the middle tap end of the first secondary winding 212, so the rectifying unit 220 can extract a part of the output voltage difference of the secondary side of the transformer 210. The rectifying unit 220 outputs a second power signal V2 with a smaller voltage, and the second power signal V2 is filtered by the capacitor C1 and then transmitted to the feedback unit 230, so that the second power signal V2 can drive the load 300 with a smaller power requirement.

As shown in fig. 7, since the first switch Q1 is controlled by the feedback unit 230 to be turned on and the second switch Q2 is controlled by the feedback unit 230 to be turned off, when the current path from the transformer 210 to the load 300 flows through the lower side of the second secondary winding 213 from the middle tap end 214, the current flows through the diode D3, the capacitor C1, the load 300, the inductive current element CS1 and the first switch Q1. Fig. 6 and 7 are schematic diagrams of the rectifying unit 220 under the half-bridge rectification mode, which are different only in that the transformer current direction is opposite and the current flows through the diode.

When the second power signal V2 detected by the feedback unit 230 is greater than the reference voltage set by the internal circuit of the feedback unit 230, the control signal is output to turn off the first switch Q1 and turn on the second switch Q2, so that the current path of the power switching circuit 200 is as shown in fig. 4 and 5.

In some embodiments, when the second power signal V2 detected by the feedback unit 230 is smaller than the reference voltage set by the internal circuit of the feedback unit 230, the output control signal turns on the first switch Q1 and turns off the second switch Q2, so that the current path of the power switching circuit 200 is as shown in fig. 6 and fig. 7.

Because the switching units disposed in the power switching circuit 200 may be different in different types under different practical conditions, the on and off conditions of the switching units are also different. For example, the switching unit may be a P-type mosfet, an N-type mosfet, or a bipolar junction transistor. Because different switches are set according to actual requirements, the control signal output by the feedback unit 230 can be adjusted differently according to the on or off condition of different switches.

The above embodiments are merely illustrative of the switching circuit principle, the switching conditions and the method of the power switching circuit 200, but the invention is not limited thereto. In other embodiments, referring to fig. 8, the power switching circuit 200 includes a transformer 210, a rectifying unit 220 composed of diodes D1, D2, D3, and D4, a first switching unit 240, a second switching unit 250, a capacitor C1, an inductive current element CS1, and a feedback unit 230. Wherein the first switching unit 240 includes a first switch Q1 and the second switching unit 250 includes a third switch Q3 and a fourth switch Q4.

In some embodiments, as shown in fig. 8, a first terminal of the third switch Q3 of the second switching unit 250 is coupled to an anode terminal of the diode D2, a second terminal of the third switch Q3 is coupled to a second terminal of the first switch Q1 and a second terminal of the fourth switch Q4, and a first terminal of the fourth switch Q4 of the second switching unit 250 is coupled to an anode terminal of the diode D4.

In some embodiments, as shown in fig. 8, the feedback unit 230 outputs the control signal and enables the third switch Q3 and the fourth switch Q4 of the second switching unit 250 to be turned on or off simultaneously.

When the second power signal V2 detected by the feedback unit 230 is greater than the reference voltage set by the internal circuit of the feedback unit 230, the control signal is output to turn off the first switch Q1 of the first switching unit 240 and turn on the third switch Q3 and the fourth switch Q4 of the second switching unit 250, so that the current path of the power switching circuit 200 is the same as the case shown in fig. 4 and 5.

In some embodiments, when the second power signal V2 detected by the feedback unit 230 is less than the reference voltage set by the internal circuit of the feedback unit 230, the output control signal turns on the first switch Q1 of the first switching unit 240 and turns off the third switch Q3 and the fourth switch Q4 of the second switching unit 250, so that the current path of the power switching circuit 200 is the same as the case shown in fig. 6 and 7.

The connection relationship and operation details of other circuit elements in the power switching circuit 200 are substantially similar to those of the power switching circuit 200 in the embodiment of fig. 2, and are not repeated herein.

Referring to fig. 9, fig. 9 is a circuit diagram of another power converter 100 according to an embodiment of the present disclosure. In fig. 9, similar components related to the embodiment of fig. 2 are denoted by the same reference numerals for easy understanding, and the specific principles of the similar components have been described in detail in the previous paragraphs. In the embodiment shown in fig. 9, the power switching circuit 200 includes a first resonant capacitor Cr1 and a second resonant capacitor Cr2, the first resonant capacitor Cr1 is coupled between the upper side of the first secondary winding 212 and the middle tap end 214, i.e. in parallel with the first secondary winding 212, and the second resonant capacitor Cr2 is coupled between the lower side of the second secondary winding 213 and the middle tap end 214, i.e. in parallel with the second secondary winding 213. The first resonant capacitor Cr1 and the second resonant capacitor Cr2 may replace the resonant function of the resonant capacitor Cr in the resonant circuit 110 of fig. 2.

In some embodiments, the first resonant capacitor Cr1 and the second resonant capacitor Cr2 in the power switching circuit 200 may not only replace the resonant function of the resonant capacitor Cr in the resonant circuit 110, but also have a current stabilizing function. This has the advantage that improving the output current of the resonant circuit has the disadvantage of significant current ripple.

In some other embodiments, the LCC resonant circuit 110 of fig. 2 may also be an LLC resonant circuit, wherein the resonant function of the resonant capacitor in the LLC resonant circuit may also be replaced by the first resonant capacitor Cr1 and/or the second resonant capacitor Cr2 in fig. 9. In addition, the resonant circuit 110 is not limited to the LCC resonant circuit or the LLC resonant circuit. The first resonant capacitor Cr1 and the second resonant capacitor Cr2 may also replace the resonant function of other resonant circuits.

In the previous embodiment, the sensing current element CS1 of the power switching circuit 200 includes a resistor, and the feedback unit 230 is used to measure the current passing through the resistor, but the present disclosure is not limited to the way that the feedback unit 230 detects the output current. Referring to fig. 10, fig. 10 is a circuit diagram of another power converter 100 according to an embodiment of the disclosure. In fig. 10, similar components related to the embodiment of fig. 2 are denoted by the same reference numerals for easy understanding, and the specific principles of the similar components have been described in detail in the previous paragraphs. In the embodiment shown in fig. 10, the power switching circuit 200 in the power converter 100 includes an inductive current element CS 2. Unlike the previous embodiment, in the embodiment of fig. 10, the sensing current element CS2 includes a current transformer, which can be used to detect the passing current and report the passing current to the feedback unit 230. In the embodiment of fig. 10, one side of the sense current element CS2 is coupled to the cathode terminal of the diode D1 and the cathode terminal of the diode D3 of the rectifying unit 220, the other side of the sense current element CS2 is coupled to the load 300 and the first terminal of the capacitor C1, and the second terminal of the capacitor C1 is coupled to the anode terminal of the diode D2 and the anode terminal of the diode D4. The sense current element CS2 can sense the magnitude of the output current flowing to the load 300 from the cathode terminal of the diode D1 and the cathode terminal of the diode D3. Accordingly, the feedback unit 230 can measure the magnitude of the current passing through the sense current element CS2 and the voltage of the second power signal V2, so as to control the switching states of the first switching unit 240 and the second switching unit 250.

Furthermore, the features and circuits in the various figures, embodiments and embodiments of this disclosure may be combined with each other without conflict. The circuits shown in the drawings are for illustrative purposes only and are simplified to simplify the explanation and facilitate understanding, but are not intended to limit the present disclosure.

In addition, those skilled in the art will understand that, in various embodiments, each circuit unit may be implemented by various types of digital or analog circuits, and may also be implemented by different integrated circuit chips. The various components may also be integrated into a single integrated circuit chip. The above description is merely exemplary, and the present disclosure is not limited thereto. Electronic components such as resistors, capacitors, diodes, transistor switches, etc. may be implemented by any suitable means. For example, the switches Q1-Q4 may be implemented by Metal-Oxide-Semiconductor Field-Effect transistors (MOSFETs), Bipolar Junction Transistors (BJTs) or other types of transistors as desired.

Claims

1. A power switching circuit, comprising:

a transformer for outputting a first power signal, the transformer having a middle tap end;

a rectifier unit coupled to the transformer for receiving the first power signal and outputting a second power signal;

a first switching unit coupled to the rectifying unit and the middle tap end of the transformer;

a second switching unit coupled to the rectifying unit and the first switching unit; and

a feedback unit for receiving the second power signal and controlling the first switching unit and the second switching unit.

2. The power switching circuit of claim 1, wherein the feedback unit controls the first switching unit to be turned off and the second switching unit to be turned on when a voltage level of the second power signal received by the feedback unit is greater than a reference voltage,

when the voltage level of the second power signal received by the feedback unit is less than the reference voltage, the feedback unit controls the first switching unit to be turned on and the second switching unit to be turned off.

3. The power switching circuit of claim 1, wherein the power switching circuit comprises a resonant circuit, the transformer comprises a primary winding, a first secondary winding, a second secondary winding and the middle tap, the primary winding is coupled to the resonant circuit, and the first secondary winding and the second secondary winding are coupled to the rectifying unit.

4. The power switching circuit of claim 3, wherein the power switching circuit comprises a first resonant capacitor connected in parallel with the first secondary winding and a second resonant capacitor connected in parallel with the second secondary winding.

5. The power switching circuit of claim 1, wherein the rectifying unit comprises a first diode, a second diode, a third diode, and a fourth diode, wherein an anode of the first diode is electrically coupled to the first secondary winding and a cathode of the second diode, a cathode of the first diode is electrically coupled to a cathode of the third diode, an anode of the second diode is electrically coupled to an anode of the fourth diode, and an anode of the third diode, a cathode of the fourth diode, and the second secondary winding are coupled to each other.

6. The power switching circuit of claim 5, wherein the first switching unit comprises a first switch, the second switching unit comprises a second switch, a first terminal of the first switch is coupled to the middle tap of the transformer, a control terminal of the first switch is coupled to the feedback unit, a second terminal of the first switch and a second terminal of the second switch are coupled to a load, a first terminal of the second switch is coupled to the anode terminal of the second diode and the anode terminal of the fourth diode, and a control terminal of the second switch is coupled to the feedback unit.

7. The power switching circuit of claim 5, wherein the first switching unit comprises a first switch, the second switching unit comprises a third switch and a fourth switch, a first terminal of the first switch is coupled to the middle tap of the transformer, a control terminal of the first switch is coupled to the feedback unit, a second terminal of the first switch is coupled to a load, a first terminal of the third switch is coupled to the anode terminal of the second diode, a second terminal of the third switch is coupled to the second terminal of the first switch, a control terminal of the third switch is coupled to the feedback unit, a first terminal of the fourth switch is coupled to the anode terminal of the fourth diode, a second terminal of the fourth switch is coupled to the second terminal of the first switch, and a control terminal of the fourth switch is coupled to the feedback unit.

8. The power switching circuit of claim 5, further comprising a capacitor and a sense current element, wherein a first terminal of the capacitor is coupled to the cathode terminal of the first diode and the cathode terminal of the third diode, a second terminal of the capacitor is coupled to the sense current element, and the sense current element is coupled to the first switching unit and the second switching unit.

9. The power switching circuit of claim 5, further comprising a capacitor and a sense current element, wherein a first side of the sense current element is coupled to the cathode of the first diode and the cathode of the third diode, a second side of the sense current element is coupled to a first end of the capacitor, and a second end of the capacitor is coupled to the anode of the second diode and the anode of the fourth diode.

10. The power switching circuit according to claim 8 or 9, wherein the feedback unit comprises a first receiving terminal, a second receiving terminal, a first output terminal, and a second output terminal, the first receiving terminal is electrically coupled to the first terminal of the capacitor and is configured to receive the second power signal output by the rectifying unit, the second receiving terminal is coupled to the inductive current element and is configured to receive a current signal formed by the second power signal flowing through the inductive current element, the first output terminal is coupled to the first switching unit, and the second output terminal is coupled to the second switching unit.

11. The power switching circuit according to claim 1, wherein when a voltage level of the second power signal received by the feedback unit is greater than the reference voltage, the feedback unit controls the first switching unit to be turned off and the second switching unit to be turned on, so that the rectifying unit operates in a full-bridge rectification mode, and when a voltage level of the second power signal received by the feedback unit is less than the reference voltage, the feedback unit controls the first switching unit to be turned on and the second switching unit to be turned off, so that the rectifying unit operates in a half-bridge rectification mode.

12. A switching method of a power switching circuit, the power switching circuit comprising a transformer, a rectifying unit, a first switching unit and a second switching unit, the transformer comprising a middle tap, the rectifying unit coupled to the transformer for providing a second power signal, the first switching unit coupled between the middle tap and a load, the second switching unit coupled between the rectifying unit and the load, the switching method comprising:

detecting a voltage level of the second power signal, and determining whether the first switching unit and the second switching unit are turned on or off.

13. The method of claim 12, wherein turning off the first switching unit and turning on the second switching unit when the voltage level of the second power signal is greater than a reference voltage; and

when the voltage level of the second power signal is less than the reference voltage, the first switching unit is turned on and the second switching unit is turned off.

14. The handover method of claim 12, wherein:

when a voltage level of the second power signal is greater than a reference voltage, the first switching unit is turned off and the second switching unit is turned on, so that the rectifying unit works in a full-bridge rectification type;

when a voltage level of the second power signal received by the feedback unit is less than the reference voltage, the first switching unit is turned on and the second switching unit is turned off, so that the rectifying unit works in a half-bridge rectification type.